1. Technical Field
This invention generally relates to finger joint cutter heads which are mounted on a rotatable shaper spindle, such that the cutter head cuts finger joints in the edges of wood products for joining two such products together. More particularly, this invention relates to a cutter blade for use in a finger joint cutter head. Cooperating finger joint cuts are used to join two pieces of material, generally wood, together to form one continuous larger piece. Finger joint cutting is an economical process to produce a long piece from a number of short pieces by providing matching or cooperating surfaces at the ends of the pieces which can be fitted together and glued.
2. Background
U.S. Pat. No. 3,951,189 to Cromeens, incorporated herein by reference, discloses an apparatus for carrying out this process. Generally, a finger joint cutter head is mounted on the spindle of a shaper apparatus through which the shorter pieces of material are fed.
U.S. Pat. No. 5,005,619 to Jensen, also incorporated herein by reference, discloses the details of the construction of several cutter heads. Generally speaking a plurality of individual claw-shaped cutter blades are stacked one on top of another to form cutter blade assemblies which in turn are annularly secured via bolts between the top and bottom plate of the cutter head. The top and bottom plates are attached in parallel spaced relation to an arbor collar. The top and bottom plates extend radially outward from the arbor collar.
Initially, the individually cutter blades were simply machined from a high speed tool steel. The actual cutting surface or tip was simply a ground surface of the tool steel. These blades had a very limited life and had to be regularly sharpened because of the high speed, high temperature and abrasive nature of their use.
In response to this problem, harder cutting surfaces or tips, such as tungsten carbide, were attached to the cutter blade to serve as the actual cutting surface. FIG. 2 of the drawings illustrates this prior art cutter blade, generally designated as one. Prior art cutter blade 1 has a high speed tool steel backing 2 to which carbide tip 3 is attached via a silver alloy braze joint 4, or other suitable attachment mechanism. As can be seen from FIG. 2, the innermost end of carbide tip 3 is rounded to mate with the fillet on backing 2. This cutter blade configuration represents the current state of the art.
While this cutter blade demonstrates tremendous improvement over the previous all steel cutter since it does not require the frequent resharpening, it is still prone to failure. Because of the different expansion coefficients of the carbide material and steel backing, a carbide tip must be carefully attached to the steel backing. This is especially true since heat is generally used to accomplish the attachment process, as in brazing or welding. Currently, a copper strip which is clad on both sides with a silver alloy braze material is used to bond the carbide tip to the steel backing. This so called "sandwich" braze helps prevent bond failure or cracking of the carbide as the two distinct materials are cooled at the end of the brazing process. The copper strip acts as a mechanical stress buffer.
As can readily be seen from FIG. 2, the area of carbide tip 4 which is actually bonded to steel backing 2, this surface of the backing member is hereinafter referred to as the cutter tip attachment surface, is approximately equal or slightly greater than the actual cutting surface presented by the blade. This is unfortunate in that virtually all of the force generated during cutting is transferred through the braze joint to steel backing 2. This fact, when coupled with the high temperatures generated during the cutting process, results in an unacceptably high failure rate of the cutter blades.
What is needed is a cutter blade for finger joint cutting which does not require frequent sharpening and which prolongs the life of the cutter blades. It is, therefore, an object of this invention to provide a carbide tipped, or other hard material tipped, finger joint cutter blade which is not as susceptible to failure.